Electrically-powered devices and apparatus are widely used, at least because of their convenience and ease of operation. One need only browse through a commercial restaurant equipment store or the small appliance section of a modern department store to find numerous examples of electrically-powered products for residential and commercial use.
Some of these appliances have electric motors; others use electric heating devices for cooking food, brewing beverages and the like. An example of an appliance of the latter type is an electric urn for making brewed beverages, e.g., coffee, tea, hot spiced drinks or the like. Such urns are available in a variety of sizes with 55 and 100 cup coffee urns being very common.
"Brewing-type" electric appliances usually use two heating elements, namely, a higher-power element for brewing or "perking" the beverage and a lower-power element for post-brewing warming. The latter element keeps the beverage hot for an extended period of time during serving. Examples of prior art appliances having two heating elements are shown in the patent literature. Examples include U.S. Pat. Nos. 3,392,662 (Schwartz, Jr.), 3,836,713 (Halvorson, Sr.) and 4,147,925 (Belinkoff).
The Schwartz, Jr. patent shows a coffee percolator, the primary or brewing coil for which is embedded in a casting. The secondary coil (for post-brewing warming) appears to be wrapped around a necked-down portion of the casting. Such construction suggests a secondary operation, namely, wrapping the secondary coil, is required to make the assembly. The arrangement of the heating assembly is consistent with known technology in that the secondary warming coil is closer to the bottom of the vessel than is the primary coil.
The Halvorson, Sr. patent shows a heater assembly for a coffee percolator. Such assembly uses a "rope-like" warming coil covered with a soft, woven fabric covering. The flexible warming coil is wrapped around a rigid, cylindrical main heater body member. Such body member has a number of recesses for receiving the warming coil and the result is said to be a unitized subassembly. It is apparent from the Halvorson, Sr. patent that ease of assembly and disassembly are important considerations when designing a small appliance.
The Belinkoff patent shows a heater assembly for use with a percolator. The main brewing coil is spiral-wrapped around a well formed in the bottom of the liquid container and the warming coil (or "auxiliary" coil, as the patent calls it) is attached to and in intimate contact with a heat distribution plate at the bottom of the container. The main and auxiliary coils are in series and both coils are used for post-brewing warming. A distinct disadvantage of such heater assembly is that the required time to assemble it to the percolator is relatively long and, in view of the invention, is unnecessary.
A feature common to the apparatus shown in the Schwartz, Jr., Halvorson, Sr. and Belinkoff patents is that all of them mount the warming coil closer to the bottom of the liquid container than the main heating coil. The apparent reason for this arrangement is that since the warming coil produces substantially less heat than the main heating coil, it is thought to be necessary to mount such warming coil relatively close to the container bottom.
While the prior art heating devices have been generally satisfactory for their intended purpose, some are attended by certain disadvantages. For example, the fabric-covered warming coil like that shown in the Halvorson, Sr. patent is thought by some to be undesirable because once wet, it stays wet for some extended period.
Another disadvantage relates to relative ease of assembly. In one prior art coffee urn, the main heater unit and rope-like warming heater are separately handled during manufacture and separately mounted. The latter is attached to the urn by several clips, each of which has to be separately affixed by a screw or the like. The assembly time required to mount such warming heater is undesirably long.
Yet another disadvantage of prior art devices is that they do not address the matter of mounting auxiliary components such as thermostats. The percolator assembly of the Belinkoff patent requires a separate mounting bracket for the percolator thermostat. And as will become apparent from the descriptions of the invention, the heating device of the Belinkoff patent is unnecessarily high and increases the height of the percolator assembly with which it is used.
An improved heating device which is free of water-absorbing material, which is quick to mount and easy to wire, which has excellent heat-transfer characteristics and which readily accommodates an auxiliary device such as a thermostat and which addresses other disadvantages of prior art devices would be an important advance.